Gas detection system and method

ABSTRACT

This invention relates to a method of and system for facilitating detection of a particular predetermined gas in a scene under observation. The gas in the scene is typically associated with a gas leak in equipment. To this end, the system comprises an infrared camera arrangement; a strobing illuminator device having a strobing frequency matched to a frame rate of the camera; and a processing arrangement. The processing arrangement is configured to store a prior frame obtained via the infrared camera arrangement; and compare a current frame with the stored prior frame and generate an output signal in response to said comparison. The system also comprises a display device configured to display an output image based at least on the output signal generated by the processing arrangement so as to facilitate detection of the particular predetermined gas, in use.

FIELD OF INVENTION

THIS INVENTION relates to gas detection systems and methods of gasdetection, particularly gas leakage detection systems and methods ofdetecting gas leakage from equipment.

BACKGROUND TO THE INVENTION

In various industries, undesirable gas leaks from equipment, forexample, equipment in power distribution systems, are undesirable forvarious reasons, for example, safety, environmental, operationalrequirements, and the like. In view of environmental reasons,environmental legislation in countries worldwide impose stricter stanceson spillages and pollution of hazardous and greenhouse gases. It is thusdesirable to be able to detect a gas leak and pinpoint exactly thelocation of the gas leaks so that suitable repair protocols are deployedto address the leak. For example, in the case of SF₆ that is used inelectrical installation, a loss of gas not only causes environmentalharm but also may lead to malfunctioning of the installation. A problemin detecting leaks is encountered when gas leaks (e.g., colourless gas)are against ambient backgrounds as they are imperceptible to the humaneye. These leaks often go unnoticed with undesirable outcomes.

One way of detecting such gas leaks quickly, particularly at longstand-off distances, in varying ambient backgrounds, for example, insuch as electrical, chemical, and petrochemical industries, is anOptical Gas Imaging (OGI) technique. The OGI technique makes use of agas detection camera operating at a selected wavelength so as tovisualise any gas leaks. In this way, gas leaks may be easily detectedand the necessary steps be taken to repair equipment associated withsuch leaks.

Some gas detection cameras currently in the market have means ofdetecting gas leaks by way of so called ‘passive’ gas detectiontechnology. This technology employed a cooled detector and a cooledbandpass filter in order for the camera to detect said leaks.

Other cameras such as those of the type descried in U.S. Pat. No.5,001,345 use infrared laser-illuminated imaging for the visualizationof gas plumes. In this prior art document, a laser that is constantly ONis employed to supply photons to an item (e.g., a pipe) under test beingsupplied with a preheated test gas such as SF₆. Images from narrow andwideband filters are then compared in order to detect gas leaks.

Some cameras such as those of the type described in US2015/0369730 makeuse of active illumination and passive gas detection technologies so asto be able to visualize and detect gas leaks. However, the Applicant hasnoted difficulty in detecting gas leaks in these systems when thebackground radiated photons and the photon traveling through the gascloud is very similar. Moreover, these so-called conventionalactive/passive systems are very slow from a processing perspective andrequire that the camera be kept very still as movement thereof willimpact on accuracy of the detection.

In this regard, it is thus an object of the present invention to addressthese need/s and/or to be able to better detect gas leaks and/or detectgas leaks in a different manner.

SUMMARY OF THE INVENTION

According to a first aspect of the invention, there is provided a systemfor detecting or facilitating detection of a predetermined gas in ascene under observation, wherein the system comprises:

-   -   an infrared camera arrangement configured to acquire infrared        images of the scene under observation at a predetermined frame        rate;    -   an illuminator device configured to radiate photons at a        predetermined wavelength to the scene under observation, wherein        the illuminator device is strobed at a predetermined strobing        frequency between an ON state in which photons at the        predetermined wavelength are radiated to the scene under        observation, and an OFF state in which photons of the        predetermined wavelength are not radiated to the scene under        observation, and wherein the strobing frequency of the        illuminator device is associated with the predetermined frame        rate of the infrared camera arrangement such that active        infrared images are acquired by the infrared camera arrangement        during the ON state of the illuminator device and passive        infrared images are acquired by the infrared camera arrangement        during the OFF state of the illuminator device in an alternating        fashion at the predetermined frame rate;    -   a processing arrangement, wherein the processing arrangement        comprises:        -   data storage device configured to store at least one prior            infrared image acquired by the infrared camera arrangement,            wherein the prior infrared image is either an active            infrared image or a passive infrared image; and        -   at least one processor configured to compare at least one            current infrared image acquired by the infrared camera            arrangement with the at least one prior infrared image            stored in the data storage device and generate an output            signal in response to said comparison, wherein the current            infrared image is either a passive infrared image or an            active infrared image;    -   and        -   a display device configured to display an output image based            at least on the output signal generated by the processing            arrangement so as to facilitate detection of the particular            predetermined gas, in use.

The system may be configured to strobe the illuminator device in atemporal fashion between the ON state and the OFF state.

It will be understood that the one or more processors may be configuredto compare active and passive infrared images.

One or both of the predetermined strobing frequency and thepredetermined frame rate may be selected so that the infrared cameraarrangement may acquire at least one active image during every ON stateof the illuminator device, and at least one passive image during everyOFF state of the illuminator device.

The predetermined frame rate of the camera arrangement may be a multipleof the predetermined strobing frequency of the illuminator device. Inthis way, the camera arrangement may acquire multiple active and passiveinfrared images in each strobing cycle of the strobing frequency. Eachstrobing cycle may be understood to mean each time the illuminatordevice is operated ON and OFF.

It will be noted that the provision that “the strobing frequency of theilluminator device is associated with the predetermined frame rate ofthe infrared camera arrangement” may be understood to mean that thestrobing frequency of the illuminator device is related to thepredetermined frame rate of the infrared camera arrangement. In thisway, the acquiring of infrared images during the strobing of theilluminator device is effectively calibrated thus improving thesensitivity of the system as described herein.

In one example embodiment, the predetermined frame rate of the infraredcamera arrangement may be an even multiple of the strobing frequency. Inthis way, as alluded to above, the same number of active infrared imagesare compared with the same number of passive infrared images areacquired in a particular cycle of the of strobing of the illuminatordevice. For example, the predetermined frame rate may be at least twiceor four times that of the predetermined strobing frequency. In this way,the infrared camera arrangement may acquire one or two active infraredimages during the ON state of the illuminator device. Similarly, thecamera arrangement may acquire one or two passive infrared image duringthe OFF state of the illuminator device in an alternating fashion,continuously during operation of the system. Thus, the processorarrangement may be configured to compare the same number of active andpassive images in one strobing cycle. It will be noted that theprocessor arrangement may be configured to compare active and passiveinfrared image/s in each strobing cycle of the illuminator device.

The illuminator device and the infrared camera arrangement may besynchronized so that active images are acquired in the ON state of theilluminator device and passive images are acquired in the OFF state ofthe illuminator device in an alternating continuous fashion. In thisway, the processor arrangement effectively is certain to capture thedesired active and passive infrared images during a particular strobingcycle.

Though it is mentioned that the processor arrangement is configured tocompare at least one active and passive infrared image, it will beunderstood that the processor arrangement may be configured to comparemore than one active and passive infrared images.

The system may comprise a shutter which is any one of an electronicshutter, a mechanical shutter, and an electro-mechanical shutterconfigured to strobe the illuminator device.

The processor arrangement may be configured to compare the at least onecurrent frame and the at least one prior frame by determining thedifference/s between the at least one current frame and the at least oneprior frame, wherein output signal corresponds to an infrared imagerepresentative of the difference/s between the at least one currentinfrared image and the at least one prior infrared image.

The processor may be configured to compare the at least one currentinfrared image or frame and the at least one prior infrared image orframe by subtracting the same from each other. The output signal maythus be representative of the differences between the current frame andthe prior frame. It will be understood that in some example embodiments,the processor may make use of other techniques, for example, otherconventional image processing techniques to compare frames.

The infrared camera arrangement may comprise a single narrow bandwidthfilter centered substantially at, or around, a gas absorption wavelengthof the particular predetermined gas selected for detection.

The infrared camera arrangement may be an infrared video cameraarrangement configured to acquire infrared video images. These imagesmay be acquired in a continuous fashion.

The infrared camera arrangement may comprise:

-   -   a detector comprising an array of quantum-well infrared photo        detectors configured to generate an electrical signal in        response to a photon being received thereby;    -   a lens having a field of view, wherein the lens is configured to        collect photons from a scene under observation and project the        photons onto the detector; and    -   a cooling engine configured to control the temperature of the        detector, and the optical filter to be at, or around,        predetermined temperatures, respectively;    -   wherein the infrared camera arrangement is configured to        generate infrared images of the scene under observation based on        electrical signals generated by the detector.

The predetermined wavelength of the photons radiated by the illuminatordevice may be at, or around, a gas absorption wavelength of theparticular predetermined gas selected for detection.

The detector, and lens may be selected based on a gas absorptionwavelength of the particular predetermined gas selected for detection.

The detector may comprise a two dimensional array of quantum-wellinfrared photo detectors. The quantum-well infrared photo detectors mayhave an operative surface and are configured to generate electricalsignals in the form of photocurrent in response to an irradiance on theoperative surface thereof. The quantum-well infrared photo detectors mayhave a quantum efficiency based on the particular selected gas fordetection.

The infrared camera arrangement may be configured to convertphotocurrent from the detector to digital signals representative ofinfrared images of the scene under observation.

The quantum-well infrared photo detectors may comprise layers of GalliumArsenide, and Aluminium Gallium Arsenide. The lens may be constructed ofGermanium, or a combination of Germanium and Silicon.

The aforementioned filter may be integrated with the detector.

The cooling engine may be configured to cool the detector to andmaintain the detector at a temperature between a range of 60 K and 75 K.The cooling engine may be configured to cool the optical filter to andmaintain the optical filter at a temperature between a range of 85 K and95 K.

The cooling engine may be configured to maintain the detector atapproximately 62 K or 70 K. The cooling engine may be configured tomaintain the optical filter at approximately 90 K.

The system may comprise a visible light camera arrangement configured toacquire visible light images of the scene under observation. Theinfrared camera arrangement and the visible light camera arrangement mayhave substantially the same or similar field of view.

The visible light camera arrangement may be a visible light video cameraarrangement configured to acquire visible light video images.

The processing arrangement may be configured to combine the outputsignal generated thereby with an output from the visible light cameraarrangement to generate a combined signal representative of an infraredimage of the scene under observation superimposed onto a visible imageof the scene under observation. The combined signal may correspond tothe output image displayed by the display device.

The processing arrangement may be configured to:

-   -   receive an electrical signal from the detector;    -   generate an infrared image based on the electrical signal        received from the detector; and    -   clean the generated infrared image by one or more of removing,        replacing, and correcting pixels of the generated image which do        not meet predetermined characteristics so as to generate a        cleaned infrared image.

The illuminator device may be selected from a group comprising aninfrared illuminator, and a laser. The infrared illuminator may be inthe form of a heated electrical filament arrangement, and wherein thelaser is in the form of a quantum cascade laser. The predeterminedwavelength at which the illuminator device radiates photons may be basedon the predetermined gas to be detected.

The system may be provided in a housing. The housing may define athermally insulated compartment for enclosing all or a majority of thecomponents of the infrared camera arrangement. The system may comprise asuitable cooling arrangement to cool at least components located in thehousing.

The system may comprise a user interaction module comprising suitableactuators located on one or more outer surfaces of the housing, whereinoperation of the actuators generate suitable command signals forcontrolling the system.

The display device may be provided within the housing, and wherein thehousing comprises an eyepiece aligned with the display device so thatusers may view the display device within the housing via the eye-piece.As described herein the eye-piece may be a dual eye-piece to allow auser to view the display device with both eyes, in use. As will bedescribed below, the display device may be in the form of a liquidcrystal display (LCD), light emitting diode (LED) display, organic LED(OLED) display, or the like.

The system may comprise a re-chargeable power supply unit configured topower the electrical or electronic components of the system.

The system may comprise a laser pointer to assist a user to orient thesystem to the scene under observation.

The frame rate of the infrared camera arrangement may be between 15 Hzand 60 Hz. The illuminator device may be strobed at a matching frequency(strobing frequency) of between 15 Hz and 60 Hz. However, it will benoted that the illuminator device may be strobed at other strobingfrequencies depending on the particular example embodiment in question.

According to a second aspect of the invention, there is provided amethod for detecting a particular predetermined gas in a scene underobservation or for facilitating the detection of the presence of aparticular predetermined gas, the method comprising:

-   -   radiating photons at a predetermined wavelength towards a scene        under observation in a strobed fashion at a predetermined        strobing frequency such that photons at the predetermined        wavelength are radiated to the scene under observation, and        photons at the predetermined wavelength are not radiated to the        scene under observation in an alternating fashion according to        the predetermined strobing frequency;    -   acquiring infrared images from the scene under observation at a        predetermined frame rate, wherein the predetermined frame rate        is associated with the predetermined strobing frequency such        that active infrared images are acquired while photons at the        predetermined wavelength are radiated to the scene under        observation, and passive infrared images are acquired while        photons at the predetermined wavelength are not radiated to the        scene under observation in an alternating fashion at the        predetermined frame rate;    -   storing at least one prior infrared image acquired from the        scene under observation, wherein the at least one prior infrared        image is either an active infrared image or a passive infrared        image,    -   comparing at least one current infrared image acquired with the        stored at least one prior infrared image, wherein the at least        one prior infrared image is either a passive infrared image or        an active infrared image;    -   generating an output signal in response to said comparison; and    -   displaying an output image on a display device based at least on        the generated output signal so as to facilitate detection of the        particular predetermined gas.

The method may comprise the step of radiating photons for apredetermined period of time towards the scene and simultaneouslyacquiring an active infrared image of the scene, and stopping radiatingphotons for a predetermined period of time towards the scene andsimultaneously acquiring a passive infrared image of the scene, whereinthe active and passive images are acquired at the predetermined framerate, and the predetermined periods of time where photons are radiatedor stopped is based on at the predetermined frequency of strobing.

The method may comprise radiating photons at the predeterminedwavelength towards the scene for a predetermined period of time andsimultaneously acquiring an active infrared image of the scene, and notradiating photons at the predetermined wavelength towards the scene fora predetermined period of time and simultaneously acquiring a passiveinfrared image of the scene, wherein the active and passive images areacquired at the predetermined frame rate, and the predetermined periodsof time where photons are radiated towards the scene or not are based onthe predetermined strobing frequency.

It will be appreciated that the method may comprise radiating photons bycontrolling an illuminator device as described above to radiate photonsin a strobed fashion at the predetermined frequency.

The method may comprise comparing the at least one current frame and theat least one prior frame by determining the difference/s between the atleast one current frame and the at least one prior frame, wherein outputsignal corresponds to an infrared image representative of thedifference/s between the at least one current infrared image and the atleast one prior infrared image.

The method may comprise comparing the current frame and the prior frameby subtracting the same from each other, wherein the output signal isrepresentative of the difference between the current frame and the priorframe.

The method may comprise acquiring infrared video images.

The method may comprise:

-   -   acquiring visible light images of the scene under observation;

combining the generated output signal with a signal representative of anacquired visible light image to generate a combined signalrepresentative of an infrared image of the scene under observationsuperimposed onto a visible image of the scene under observation; and

-   -   displaying the combined signal on the display device.

The method may comprise acquiring visible light video images.

The method may comprise:

-   -   radiating photons at a predetermined wavelength towards the        scene under observation;    -   collecting photons from the scene under observation with a lens        having a field of view;    -   projecting, with the lens, photons collected to a detector;

filtering photons projected from the lens with an optical filter therebyto allow only projected photons at a predetermined wavelength to passthrough to the detector;

-   -   generating electrical signals in response to filtered photons of        a predetermined wavelength being received by the detector; and    -   generating an infrared image of the scene under observation        based on the electrical signals received from the detector so as        to enable detection of the gas, in use.

The method may comprise controlling the temperature of the detector, andthe optical filter to be at, or around, predetermined temperatures,respectively.

The predetermined wavelength associated with the steps of radiatingphotons, filtering photons, and generating electrical signals may be at,or around, a gas absorption wavelength of the particular predeterminedgas selected for detection.

The method may comprise:

-   -   generating electrical signals in the form of photocurrent in        response to an irradiance on an operative surface of the        detector;    -   converting photocurrent to digital signals; and    -   generating infrared images of the scene under observation based        on the digital signals.

The method may comprise cooling the detector to and maintaining thedetector at a temperature between a range of 60 K and 75 K. The methodmay comprise cooling the optical filter to and maintaining the opticalfilter at a temperature between a range of 85 K and 95 K.

The predetermined frame rate may be a multiple of the predeterminedstrobing frequency. The predetermined frame rate may be approximatelytwice or four times the predetermined strobing frequency. The method maycomprise comparing more than one active and passive infrared images.

The method may comprise synchronizing the steps of radiating photons andacquiring infrared images. In this way, active infrared images areacquired when photons of the predetermined wavelength are radiated tothe scene and passive infrared images are acquired captured when nophotons of the predetermined wavelength are radiated to the scene. Inthis regard, it will be understood by those skilled in the art thataspects described above with respect of the first aspect of theinvention apply mutatis mutandis to the second and third aspects of theinvention described herein.

The method may comprises maintaining the detector at approximately 62Kor 70K, and maintaining the optical filter at approximately 90K.

The method may comprise:

-   -   generating a live visible video image of the scene under        observation;    -   processing generated output signals representative of at least        one output infrared image; and    -   overlaying processed at least one output infrared image        corresponding to the processed output signals onto the generated        live visible video image and/or an infrared image of the scene        under observation thereby generating an infrared overlay video        image of the scene under observation.

The step of processing the generated output signals representative ofthe at least one output image may comprise colour coding differencesbetween compared active and passive frames, wherein the processed outputinfrared image is a colour coded image to be overlaid onto the generatedlive video image. Moreover, it will be noted that the step of processingthe generated output signals representative of the at least one outputimage may comprise colour coding differences between compared active andpassive frames, wherein the processed output infrared image is a colourcoded image to be overlaid onto an infrared video image.

The method may comprise cleaning the generated infrared image by one ormore of removing, replacing, and correcting pixels of the generatedimage which do not meet predetermined characteristics so as to generatea cleaned infrared image.

The method may comprise controlling an illuminator device selected froma group comprising an infrared illuminator, and a laser to radiatephotons at, or around, a gas absorption wavelength of the particularpredetermined gas selected for detection towards the scene underobservation.

According to a third aspect of the invention, there is provided anon-transitory computer readable storage medium storing one or morecomputer executable instructions which when executed on one or moreprocessors causes the one or more processors to perform the methoddescribed herein.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a schematic diagram of a system in accordance with anexample embodiment of the invention for facilitating detection of apredetermined gas;

FIG. 2 shows an example illustration of portions of the system of FIG. 1, in use, in facilitating detection of a predetermined gas;

FIG. 3 shows an example illustration of the illumination and IR imageacquisition or capture protocol employed in the system in accordancewith an example embodiment of the invention

FIG. 4 shows portions of the system of FIG. 1 , in use, in facilitatingdetection of a predetermined gas, particularly showing the photon fluxreceived by the infrared camera arrangement;

FIG. 5 shows another example illustration of portions of the system ofFIG. 1 , in use, in facilitating detection of a predetermined gas, alsoshowing the photon flux emitted or radiated by the illuminator deviceand the photon flux received by the infrared camera arrangement;

FIG. 6 shows a flow diagram of a method for facilitating the detectionof gas in accordance with an example embodiment of the invention; and

FIG. 7 shows a diagrammatic representation of a machine in the exampleform of a computer system in which a set of instructions for causing themachine to perform any one or more of the methodologies discussedherein, may be executed.

DETAILED DESCRIPTION OF THE DRAWINGS

In the following description, for purposes of explanation, numerousspecific details are set forth in order to provide a thoroughunderstanding of an embodiment of the present disclosure. It will beevident, however, to one skilled in the art that the present disclosuremay be practiced without these specific details.

Referring to FIGS. 1 to 4 of the drawings a system for facilitating thedetection of a predetermined gas is generally indicated by referencenumeral 10. In particular, the system 10 is for imaging a scene underobservation with the camera and also imaging a predetermined gas havinga predetermined absorption wavelength in the scene. In this way, lookingat FIG. 2 , a user of the system 10 may be able to detect that there isa gas leak G in the scene under observation, or not. In particular,hazardous gas leaks G may be detected in equipment, for example, pipes Passociated with high voltage installations, prior to seriousenvironmental and/or personal harm is caused thereby which is difficultto image or determined if in front of a background B, for example, anambient background.

To this end, the system 10 may be a camera system 10 or alternately andinterchangeably referred to as an imaging system 10 for imaging a gas ofa particular pre-determined wavelength in a scene under observation. Ina preferred example embodiment, the system 10 is enclosed in a handheldand/or mountable camera having a housing which houses the variouscomponents of the system 10 discussed below. Instead, the variouscomponents of the system 10 may be spread out, for example,geographically. In the case of the latter, the geographically spacedcomponents of the system 10 may be communicatively coupled to eachother, as the case may be, to achieve the functionality describedherein. Notwithstanding, the system 10 will be described below asembodied in an apparatus comprising the various components of the system10 enclosed in a housing.

Turning to FIG. 1 , in particular, the system 10 comprises an infrared(IR) camera arrangement 12 configured to acquire infrared (IR) images ofa scene under observation 14 at a predetermined frame rate. By“acquiring images”, is also meant to include capturing/receiving imagesor acquiring electrical signals representative of IR images of a sceneunder observation. The frame rate of the arrangement 12 may be thefrequency at which IR images or IR frames are acquired or captured bythe arrangement 12.

In one example embodiment, the frame rate of the arrangement 12 isbetween 7.5 Hz and 30 Hz. In other example embodiments, the frame rateof the arrangement 12 is typically between 15 Hz and 60 Hz. The framerate may be understood to mean the frequency at which the frames orimages are acquired by the arrangement 12.

The IR camera arrangement 12 is an IR video camera arrangement 12configured to acquire infrared video images. This may be on a frame byframe basis where each frame acquired is an image.

In one example embodiment, in order to acquire IR images of the scene14, the arrangement 12 comprises a detector 16 comprising an array ofquantum-well infrared photo detectors (not shown) configured to generatean electrical signal in response to a photon being received thereby. Inone example embodiment, the detector 16 comprises a two dimensionalarray of quantum-well infrared photo detectors. The quantum-wellinfrared photo detectors have operative surfaces and are configured togenerate electrical signals in the form of photocurrent in response toirradiance on the operative surface thereof. The quantum-well infraredphoto detectors may have a quantum efficiency based on the particularselected gas for detection.

The quantum-well infrared photo detectors may comprise layers of GalliumArsenide, and Aluminium Gallium Arsenide.

A lens 18 having a field of view is coupled to the detector 16 via asingle narrow bandpass optical filter 20 centered around the absorptionwavelength of the gas to be detected. The lens 18 is configured tocollect photons from the scene under observation 14 and project thephotons onto the detector 16 via the filter 20. The lens 18 may beconstructed of Germanium, or a combination of Germanium and Silicon. Itwill be noted that the lens 18 is located on an outer surface of thehousing which holds the system 10 in the case of the same being embodiedin a single camera.

To this end, the detector 16, and lens 18 is selected based on a gasabsorption wavelength of the gas to be detected. In particular, thedetector 16, and lens 18, is matched to the gas absorption wavelength ofthe gas to be detected.

The arrangement 12 further comprises a cooling engine 23 configured tocontrol the temperature of the detector 16, and the optical filter 20 tobe at, or around, predetermined temperatures, respectively. For example,between a range of 60 K and 75 K, and/or 62 K or 70 K for the detector16, and 85 K and 95 K, particularly 90 K, for the filter 20. In someexample embodiments, the filter 20 is integrated with the detector 16.

It will be understood that the IR camera arrangement 12 is configured togenerate infrared images of the scene 14 based on electrical signalsgenerated by the detector 16. In particular, the IR camera arrangement12 is configured to convert photocurrent from the detector 16 to digitalsignals representative of infrared images of the scene underobservation.

The system 10 preferably comprises illuminator device 22 configured toradiate photons at a predetermined wavelength to the scene underobservation 16. The device 22 may radiate photons at a predeterminedwavelength which may be matched to the gas to be detected.

The device 22 may have a suitable source which radiates photons. Thedevice 22, or the source, may be in the form of an IR illuminator suchas a suitable lamp, a heated electrical filament configured to radiatephotons, a laser such as a quantum cascade laser configured to radiatephotons, or the like. To this end, the phrases “radiate photons towardsthe scene 14”, “illuminate the scene 14”, or “output light towards thescene”, etc. insofar as the illuminator device 12 is concerned allrelate to the same principle of providing photons to the scene 12.

It will be noted that the housing which houses the system 10 isconfigured to house the illuminator device 22 in a fashion so that itdirects or radiates photons to the scene 14, which scene falls in thefield of view of the arrangement 12. The wavelength of the photonsradiated by the illuminator device 22 corresponds, is particularlymatched, to the absorption wavelength of the gas to be detected.

In some example embodiments, the device 22 is a separate device from therest of the components of the system 10.

An important feature of the system 10 is that the illuminator device 22is configured to be strobed at a frequency associated with the framerate of the IR camera arrangement 12. The illuminator device 22 may becontrollably strobed. By the terms “strobing” and “strobed”, it is meantthat the illuminator device 22 is switched between ON and OFF states,wherein it radiates photons to the scene 14 in the ON state and stopsradiating photons to the scene 14 in the OFF state, in an alternatefashion. In some example embodiments, the period of the ON state and OFFstate may be the same.

The device 22 may be strobed at a frequency associated with the framerate at which the camera arrangement 12 acquires images/frame such thatthe camera arrangement 12 acquires images when the illuminator device 22is switched to the ON state as well as when the illuminator device 22 isswitched to the OFF state in a consecutive fashion. Differently stated,the camera arrangement 12 may have a frame rate at which it acquiresimages which corresponds to the frequency at which the illuminatordevice 22 is strobed such that the camera arrangement 12 acquires imageswhen the illuminator device is switched to the ON state as well as whenthe illuminator device 22 is switched to the OFF state in a consecutivefashion.

The camera arrangement 12 and the device 22 may be calibrated so thatthe arrangement 12 captures consecutive frames when the device 22 isswitched to either the ON or the OFF states in an alternating fashion.As can be best seen in FIG. 3 , the illuminator device 22 is switchedbetween ON and OFF states in a temporal fashion corresponding to theframe rate in which frames, or IR images, FRAMES 1 to 7 arecaptured/acquired. The FRAMES 1-7 are indicated for illustrativepurposes as in use there will be multiple frames acquired in thisfashion as will be well understood by those skilled in the field ofinvention. The FRAMES 1-7 captures alternate between passiveframes/images P1-P4 captured by the camera arrangement 12 whilst theilluminator device 22 is in an OFF state or in other words not radiatingphotons towards the scene 14, and active frames/images A1-A3 captured bythe arrangement 12 whilst the illuminator device 22 is an ON state or inother words radiating photons towards the scene 14. It may thus beprovided that the system 10 may operate between active and passivemodes.

It may therefore be said that the device 22 and arrangement 12 may besuitably calibrated so as to avoid scenarios where the consecutiveframes acquired by the arrangement 12 are two consecutive active orpassive frames. In other words, the device 22 and the arrangement 12 maybe synchronized. In particular, the strobing frequency of the device 22and the frame rate of the arrangement 12 may be synchronized with eachother. It will be noted that either the arrangement 12 or the device 22may be adapted so that active and passive images are consecutivelycaptured in an alternate fashion.

Strobing of the illuminator device 22 as described herein effectivelyincreases the signal (gas) to noise (background) ratio of the system 10thereby increasing the sensitivity thereof. In this regard, a user ofthe system has a wider environment range in which to use the system 10,e.g., with sky as background, pipe as background, and the like. This isof course an obvious advantage over conventional active/passivedetection schemes which do not necessarily have high signal to noiseratios which enable detection of gasses of interest with certainbackgrounds.

Also, the strobing of the illuminator device 22 is relatively fast andthus the camera does not have time to move much between frames therebyeliminating the requirement for conventional active/passive systemshaving to keep the cameras very still to increase accuracy.

The illuminator device 22 comprises a source in the form of an IRilluminator such as heated electrical filament configured to radiatephotons, and a laser such as a quantum cascade laser configured toradiate photons, or the like. To this end, the phrases “radiate photonstowards the scene 14”, “illuminate the scene 14”, or “output lighttowards the scene”, etc. insofar as the illuminator device 12 isconcerned all relate to the same principle of providing photons to thescene 12.

In one example embodiment, where the ON state and OFF state of theilluminator device 22 is concerned a single operating cycle, the cameraarrangement 12 may have a frame rate of approximately twice the strobingfrequency of the illuminator device 22 so as to acquire two images inthe single operating cycle (between ON and OFF states) of the device 22,viz., an active and passive image. In this regard, when the strobingfrequency is between 5 Hz and 30 Hz, the frame rate of the cameraarrangement 12 is approximately twice that of the strobing frequency andis therefore approximately between 10 Hz and 60 Hz so as to capture bothactive and passive images in a consecutive fashion. However, it will benoted that this need not be the case as the frame rate and strobingfrequency may be synchronized in other ratios so as to ensure that thecamera arrangement 12 acquires active and passive images consecutivelyin an alternating fashion as described herein, and illustrated in FIG. 3, at its respective frame rate.

In some example embodiments, the arrangement 12 may have a frame rate offour times that of the strobing frequency, for example, obtaining fourimages in the single operating cycle of the device 22, i.e., two activeand two passive images.

Those skilled in the field of invention will understand that the device22 may be strobed or controlled to strobe in a plurality of differentways. For example, the device 22 may be electronically controlled tostrobe by switching the source/device 22 ON and OFF according to thepredetermined strobing frequency. Instead, the system 10 may comprise asuitable mechanical/electromechanical shutter which is configured toblock light radiating from the illuminator device 22/source or directthe illuminator device 22/source away from the scene 14 to achieve thedesired strobing effect disclosed herein at the predetermined strobingfrequency. As alluded to herein, the shutter may be electronically,mechanically, or electro-mechanically controlled.

In some example embodiments, the strobing may be achieved by directingthe source toward and away from the scene 14. To this end, the device 22may be configured to direct photons to the scene 14 by pointing thesource of photons to the scene and away from the scene 14. To this end,the strobing of the illuminator device 22 may be understood to thereforemean radiating photons to the scene 14 and not radiating photons to thescene 14 in an alternate fashion, by whatever means as will beunderstood by those skilled in the field of invention.

The system 10 further comprises a processing arrangement 24. Theprocessing arrangement 24 comprises one or more processors, for example,one or more central processing units, microcontrollers, microprocessors,field programmable gate arrays (FPGAs), application specific integratedcircuits (ASICs), and the like and associated drivers, electroniccomponents, etc. to achieve the functionality described herein. Thearrangement 24 may comprise of one or more data storage devices/memorydevices such as volatile memory and/or non-volatile memory such as flashmemory, RAM (random access memory, ROM (read only memory), memory in theprocessors, or the like configured to store data including a set ofcomputer executable instructions to control operation of the system 10.The arrangement 24 may control all the data and/or signal processingoperations of the system 10. To this end, the arrangement 24 maycomprise non-transitory computer-readable storage media which storedcomputer executable instructions which when executed by one or moreprocessors, cause the same to control components of the system 10 and/orprocess data to provide outputs described herein.

To this end, though not illustrated, it will be appreciated to thoseskilled in the field that the system 10 may comprise variousconventional components such as drivers, circuitry, and other electroniccomponents to achieve the functionality described herein. Moreover, itwill be noted that the various components of the system 10 may becommunicatively coupled to either each other and/or to the arrangement24 via suitable wiring as will be well understood.

Moreover, though described as independent components, it will beappreciated that various components in the system 10 may share resourcesand/or functionality with other components and/or may be spread outacross the system 10 but described in a singular fashion whereapplicable as will be well understood by those skilled in the field ofinvention. For example, the processing arrangement 24 may be configuredto control the strobing of the illuminator device 22 in a predeterminedfashion.

In addition, the processing arrangement 24 may be configured to receivephotocurrent from the detector 16, for example, via one or more internalor external analogue to digital components and process the same togenerate digital signals representative of IR images at thepredetermined frame rate. In the case of the latter, the arrangement 12may be seen to form part of the arrangement 12. However, it will beunderstood that the arrangement 12 may alternately comprise one or moreseparate dedicated separate processors for generating images and/orsignals representative thereof and transmit the same to the processor 24for processing, though reference is made to the arrangement 24 for thispurpose for ease of explanation.

In any event, the data storage device (not shown) of the arrangement 24is typically configured to store at least one prior frame obtained viathe IR camera arrangement 12, for example, FRAME 1 (passive frame P1)which is acquired by the camera arrangement 12 is stored in the datastorage device as a prior frame in a temporal fashion (e.g., at timet-1). For ease of explanation and for clarity, it will be appreciatedthat the term “frame” may be understood to refer to an “image” capturedby the arrangement 12.

The processor arrangement 24 is configured to compare at least onecurrent frame obtained in a temporal fashion via the IR cameraarrangement 12 (e.g. at time t) with the prior frame stored in the datastorage device and generate an output signal in response to saidcomparison. For example, a current FRAME 2 may be compared with storedFRAME 1 or in other words, active frame or image A1 is compared withpassive frame or image P1, and so on in a continuous fashion. Multipleframes may be stored and associated with a consecutive temporalsequence, in use. It will be appreciated that a current frame/image maybe understood to mean a frame/image under consideration and priorframe/image may be understood to mean a frame/image which was acquiredby the arrangement immediately before the current frame/image.

It will be noted that the processor arrangement 24 is configured tocompare the current and prior frame by determining a difference betweenthe compared images, wherein the output signal is representative of thesaid difference between the compared images. The processor arrangement24 may apply conventional image processing techniques in this regard.The output signal may correspond to a processed output image which isrepresentative of the difference between the compared current and priorinfrared signals. In a preferred example embodiment, the output signalmay correspond to a processed colour coded infrared image. Or othercoloured image having pixels coloured based on the comparison. Thecoloured pixels in the processed output image may correspond to the fluxabsorbed by the gas to be detected.

To this end, it will be noted that the term “signal” as it refers toimages herein, such as infrared images, may be understood to beelectrical signals which correspond to and/or are representative ofimages as will be understood by those skilled in the field of invention.For example, the output signal generated by the processor arrangement 24may be output infrared images and/or other processed images such ascolour coded images as may be understood in the art. Differently stated,the output signals generated by the processor arrangement 24 may berepresentative of the output infrared image and/or other processedimages.

It will be understood by those skilled in the art that the arrangement24 may compare more than one active and passive images, for example, inthe case wherein the arrangement 12 captures two active and two passiveimages in one cycle of the device 22, the arrangement may compare twocurrent infrared images active/passive with two prior infrared imagespassive/active to generate the output signal.

In some example embodiments, the arrangement 12 may capture images(active and passive) of the scene during an inspection period or sessionwherein in the inspection period or session all active and passiveframes are acquired and stored. The arrangement 24 is configured tocompare current and prior frames in the temporal sequence in which theywere acquired. This may be achieved in an off-line fashion/notcompletely in real-time or in real-time.

In other example embodiments, the arrangement 12 may capture images(active and passive) of the scene during an inspection period or sessionwherein in the inspection period or session a current frame is acquiredand stored as a prior frame, and the arrangement 24 is configured tocompare the next frame (which is considered the current frame) with thestored prior frame. The stored prior frame is then discarded, e.g.,deleted from the data storage device, and the frame which was consideredthe prior frame is then stored as the prior frame. This may be done forthe duration of the inspection period. This implementation may beachieved substantially in real-time.

By comparing the active and passive images, the output signal isindicative of the absorbed flux by the gas to be detected. The outputsignal may thus be represented in various ways as described herein. Inthis regard, insofar as the flux absorbed by the gas cloud in the activeand passive images is concerned reference will be made to FIGS. 4 and 5of the drawings.

In FIG. 4 an illustration is provided which indicates the operation ofthe system 10 for acquisition of a passive image, wherein:

-   -   θ₀—ambient photon flux, determined by the environment.    -   θ₀—reflected θ₀ photon flux passing through the gas cloud, the        gas cloud will absorb some of the flux.    -   θ₅-reflected θ₀ photon flux NOT passing through the gas cloud G.

If θ₀ is reflected equally at each point;

-   -   θ₄ will be equal to θ₅ if there is no gas cloud G. If there is a        gas cloud G θ₄ will be less than θ₅ because of the gas cloud G        absorbing some of the reflected θ₀.    -   Gas absorbed flux=θ₅−θ₄

In FIG. 5 an illustration is provided which indicates the operation ofthe system 10 for acquisition of an active image, wherein:

-   -   θ₁—illuminator photon flux, determined by the illuminator.    -   θ₂—reflected θ₁ photon flux passing through the gas cloud G, the        gas cloud G will absorb some of the flux.    -   θ₃—reflected θ₁ photon flux NOT passing through the gas cloud G.

If θ₁ is reflected equally at each point;

-   -   θ₂ will be equal to θ₃ if there is no gas cloud. If there is a        gas cloud θ₂ will be less than θ₃ because of the gas absorbing        some of the reflected θ₁.    -   Gas absorbed flux=θ₃−θ₂

It follows from the foregoing that in capturing a passive image, i.e.,when the illuminator device 22 is OFF, the IR detector 16 will onlyreceive θ₄ and θ₅. However, when capturing an active image when theilluminator device 22 is on, the IR detector 16 will receive (θ₄+θ₂) and(θ₅+θ₃).

In any event, returning to FIG. 1 , the system 10 also comprises adisplay device 26 configured to display an output image based at leaston the output signal generated by the processing arrangement 24 so as tofacilitate detection of the particular predetermined gas, in use.

The display device 26 may be a conventional LED (Light Emitting Diode)display, an LCD (Liquid Crystal Display), an 0-LED (Organic LED)display, or the like.

In one example embodiment, the system 10 comprises a visible lightcamera arrangement 28 configured to acquire visible light images of thescene under observation 14. It will be appreciated that the infraredcamera arrangement 12 and the visible light camera arrangement 28 havesubstantially the same or similar field of view. The visible lightcamera arrangement 28 is typically a conventional visible light videocamera arrangement configured to acquire visible light video images. Inthis regard, the processing arrangement 24 configured to combine theoutput signal generated thereby as described above in the aforementionedcomparison with an output from the visible light camera arrangement togenerate a combined signal representative of the flux absorbed asdescribed herein superimposed onto a visible image of the scene underobservation. This may be achieved via conventional image processingtechniques well understood in the field of invention and in this way auser may easily observe a gas leak, if any, as an IR image superimposedon a visible light image.

The arrangement 24 may be configured to apply image processingtechniques to address any errors in the operation of the system 10between ON and OFF strobing states. These image processing techniquesmay be well known to those skilled in the field of image processing.

The processing described above is typically done in a streaming fashion,and substantially in real-time/near real-time, wherein output signalsgenerated continuously in response to comparison between consecutiveframes active and passive frames are continuously superimposed onto thevisible images. It will be appreciated that the visible images generatedby the arrangement 28 may be video images with a predetermined framerate which may, for example, correspond to the frame rate of the IRcamera arrangement 12.

The system 10 also include a few additional features such as a laserpointer 30 in the form of an LED (Light Emitting Diode) pointerconfigured to generate a beam of light which may be used in a selectivefashion in orienting the camera to the scene 14.

The system 10 further comprises a power source 32 in the form of are-chargeable portable battery locatable in the housing to power thesystem 10, as well as an I/O module 34 which allows data from the system10 to be transferred from and to other computing devices, etc. The I/Omodule 34 may comprise suitable ports such as serial bus ports, jackports, and the like.

Moreover, the system 10 may comprise a user interaction module 36comprising one or more buttons, dials, touchscreens, voice recognitionmodules, and the like configured to receive user inputs and transmit thesame to the processing arrangement 24 for controlling of the system 10accordingly. The module 36 may be provided at an outer surface of thehousing of the system 10 in a conventional fashion as a conventionalcamcorders and thus may comprise controls for standard features such aspan, and zoom, etc. The module 36 may in some example embodiments allowa user to be able to vary parameters of the system 10.

Turning now to FIG. 6 of the drawings where a block flow diagram of amethod in accordance with an example embodiment of the invention isgenerally indicated by reference numeral 40. The method 40 is describedwith reference to the system 10 as described above for ease ofunderstanding, but it will be appreciated by those skilled in the fieldof invention that the method 40 may be implemented by other systems, notillustrated, to achieve the functionality contemplated herein.

The method 40 is typically a method for facilitating the detection of agas as described above, for example in an electrical installation. Inthis regard, the method 40 may comprise prior steps of selecting asystem 10 matched to the gas to be detected and aiming the system 10towards the equipment. As mentioned above, various components of thesystem 10 may be selected to be suitable for use in detecting aparticular gas.

The method 40 may comprise prior steps of calibrating/synchronizing thecamera arrangement 12 and the illuminator device 22 in a manner asdescribed herein.

The method 40 then comprises radiating photons, at block 42, at apredetermined wavelength towards the scene under observation in astrobed fashion at a predetermined strobing frequency. This step may bedone by controlling the device 22 as described above using a suitableshutter and/or other means.

The method 40 comprises simultaneously as the step 42, acquiringinfrared images, at block 44, from the scene under observation at aframe rate associated with the strobing frequency by way of the cameraarrangement 12 as described above. In this way, active images areacquired during the ON state of the illuminator device 22, and passiveimages are acquired during the OFF state of the illuminator device 22 inan alternating consecutive fashion meaning that an active image isacquired after a passive image, and vice versa as illustrated in FIG. 3.

The method 40 then comprises storing, at block 46, at least a priorframe acquired from the scene 14 under observation in a data storagedevice or means. The method 40 then comprises comparing, at block 48, atleast one current frame acquired with the stored at least one priorframe by way of the processing arrangement 24 as described above, so asto generate an output signal, at block 50, in response to saidcomparison. In other words, the method 40 comprises comparing active andpassive infrared frames. These active and passive frames which arecompared are captured and compared in a temporal fashion wherein acurrent active/passive infrared frame is compared with a previouslycaptured prior passive/active infrared frame.

The step of comparing may be to determine the differences between thecurrent and prior frames, and thus the amount of flux absorbed by thetarget gas as described above. This may be achieved by subtracting thecurrent frame from the prior frame or vice versa, wherein the outputsignal is representative of the differences between the current frameand the prior frame and thus the amount of flux absorbed by the gas tobe detected.

The method 40 then comprises displaying, at block 52, an output image onthe display device 26 based at least on the generated output signal soas to facilitate detection of the particular predetermined gas. Inparticular, as alluded to above, the step 52 may comprise overlaying anIR image or other processed image such as a colour coded imagerepresentative of the generated output signal from step 50 onto anacquired visible video image so as to be able to interpret from theoverlay that a gas is present in the scene under observation 14. Theoutput signal may thus be a processed image having pixels correspondingto the flux absorbed by the gas to be detected coloured so as tofacilitate the visualization of the gas leak, if any, in use.

The method 40 may be repeated until the inspection of a scene 14 iscompleted. In other words, the method 40 may be repeated until theinspection session is over.

It will be appreciated that the system 10 may comprise of a mass storagedevice to store pictures and videos of the scene 14. These pictures andvideos can be displayed or played back or transferred to other devicesto be displayed or played back later.

The system 10 may comprise of a device to send the output image toanother device or system in real time (video streaming).

The system 10 may have a means of being remotely controlled, forexample, by way a suitable controller and receiver associated with thesystem 10, wherein the receiver is configured to receive signalsrepresentative of control signals from the controller (for example,wirelessly from a remote controller) thereby to control operation of thesystem 10.

FIG. 7 shows a diagrammatic representation of machine in the example ofa computer system 100 within which a set of instructions, for causingthe machine to perform any one or more of the methodologies discussedherein, may be executed. In other example embodiments, the machineoperates as a standalone device or may be connected (e.g., networked) toother machines. In a networked example embodiment, the machine mayoperate in the capacity of a server or a client machine in server-clientnetwork environment, or as a peer machine in a peer-to-peer (ordistributed) network environment. The machine may be a personal computer(PC), a tablet PC, a set-top box (STB), a Personal Digital Assistant(PDA), a cellular telephone, a web appliance, a network router, switchor bridge, or any machine capable of executing a set of instructions(sequential or otherwise) that specify actions to be taken by thatmachine. Further, while only a single machine is illustrated forconvenience, the term “machine” shall also be taken to include anycollection of machines, including virtual machines, that individually orjointly execute a set (or multiple sets) of instructions to perform anyone or more of the methodologies discussed herein.

In any event, the example computer system 100 includes a processor 102(e.g., a central processing unit (CPU), a graphics processing unit (GPU)or both), a main memory 104 and a static memory 106, which communicatewith each other via a bus 108. The computer system 100 may furtherinclude a video display unit 110 (e.g., a liquid crystal display (LCD)or a cathode ray tube (CRT)). The computer system 100 also includes analphanumeric input device 112 (e.g., a keyboard), a user interface (UI)navigation device 114 (e.g., a mouse, or touchpad), a disk drive unit116, a signal generation device 118 (e.g., a speaker) and a networkinterface device 120.

The disk drive unit 16 includes a machine-readable medium 122 storingone or more sets of instructions and data structures (e.g., software124) embodying or utilised by any one or more of the methodologies orfunctions described herein. The software 124 may also reside, completelyor at least partially, within the main memory 104 and/or within theprocessor 102 during execution thereof by the computer system 100, themain memory 104 and the processor 102 also constituting machine-readablemedia.

The software 124 may further be transmitted or received over a network126 via the network interface device 120 utilising any one of a numberof well-known transfer protocols (e.g., HTTP).

Although the machine-readable medium 122 is shown in an exampleembodiment to be a single medium, the term “machine-readable medium” mayrefer to a single medium or multiple media (e.g., a centralized ordistributed database, and/or associated caches and servers) that storethe one or more sets of instructions. The term “machine-readable medium”may also be taken to include any medium that is capable of storing,encoding or carrying a set of instructions for execution by the machineand that cause the machine to perform any one or more of themethodologies of the present invention, or that is capable of storing,encoding or carrying data structures utilised by or associated with sucha set of instructions. The term “machine-readable medium” mayaccordingly be taken to include, but not be limited to, solid-statememories, optical and magnetic media, and carrier wave signals.

The invention claimed is:
 1. A system for detecting a predeterminedtarget gas in a scene under observation, wherein the system comprises:an infrared camera arrangement configured to acquire infrared images ofthe scene under observation at a predetermined frame rate; anilluminator device configured to radiate photons at a predeterminedwavelength, at or around an absorption wavelength of the predeterminedtarget gas selected for detection, to the scene under observation,wherein the illuminator device is strobed at a predetermined strobingfrequency between an ON state in which photons at the predeterminedwavelength are radiated to the scene under observation, and an OFF statein which photons of the predetermined wavelength are not radiated to thescene under observation, and wherein the strobing frequency of theilluminator device is associated with the predetermined frame rate ofthe infrared camera arrangement such that active infrared images areacquired by the infrared camera arrangement during the ON state of theilluminator device and passive infrared images are acquired by theinfrared camera arrangement during the OFF state of the illuminatordevice in an alternating fashion at the predetermined frame rate; aprocessing arrangement, wherein the processing arrangement comprises: adata storage device configured to store at least one prior infraredimage acquired by the infrared camera arrangement during a prior stateof the illuminator device, wherein the prior infrared image is either anactive infrared image or a passive infrared image; and at least oneprocessor configured to compare at least one current infrared imageacquired by the infrared camera arrangement during a current state ofthe illuminator device that is different from the prior state, with theat least one prior infrared image stored in the data storage device andgenerate an output signal in response to said comparison, wherein thecurrent infrared image is either a passive infrared image or an activeinfrared image, wherein the output signal is representative of an amountof illuminator photon flux absorbed by the predetermined target gas; anda display device configured to display an output image based at least onthe output signal generated by the processing arrangement so as tofacilitate detection of the particular predetermined target gas, in use;and a handheld camera housing, wherein the infrared camera arrangementand the processing arrangement are located in the handheld camerahousing.
 2. The system as claimed in claim 1, wherein the processor isconfigured to compare the at least one current infrared image and the atleast one prior infrared image by subtracting the at least one currentinfrared image from the at least one prior infrared image or bysubtracting the at least one prior infrared image from the at least onecurrent infrared image.
 3. The system as claimed in claim 1, wherein thedata storage device is configured to store the at least one currentinfrared image as the at least one prior infrared image and the infraredcamera arrangement is configured to acquire a new at least one currentinfrared image during a next state of the illuminator device.
 4. Thesystem as claimed in claim 1, wherein the predetermined frame rate isassociated with the predetermined strobing frequency in that thepredetermined frame rate is an even multiple of the predeterminedstrobing frequency, and wherein the predetermined frame rate is at leasttwice or four times that of the predetermined strobing frequency, andwherein the infrared camera arrangement acquires multiple activeinfrared images and multiple passive infrared images in each strobingcycle of the strobing frequency.
 5. The system as claimed in claim 1,wherein the system comprises a shutter which is one of an electronicshutter, a mechanical shutter, and an electro-mechanical shutterconfigured to strobe the illuminator device.
 6. The system as claimed inclaim 1, wherein the output signal corresponds to a processed outputimage representative of the difference/s between the at least onecurrent infrared image and the at least one prior infrared image,wherein the processed output image is indicative of an amount of fluxabsorbed by the predetermined target gas to be detected.
 7. A system asclaimed in claim 1, wherein the infrared camera arrangement comprises asingle narrow bandwidth filter centered substantially at, or around, agas absorption wavelength of the particular predetermined target gasselected for detection.
 8. The system as claimed in claim 1, wherein theinfrared camera arrangement is an infrared video camera arrangementconfigured to acquire infrared video images in a continuous fashion. 9.The system as claimed in claim 8, wherein the system comprises a visiblelight camera arrangement configured to acquire visible light images ofthe scene under observation, wherein the infrared camera arrangement andthe visible light camera arrangement have substantially the same orsimilar field of view, and wherein the visible light camera arrangementis a visible light video camera arrangement configured to acquirevisible light video images.
 10. The system as claimed in claim 9,wherein the processing arrangement is configured to combine the outputsignal generated thereby with an output from the visible light cameraarrangement to generate a combined signal representative of an infraredimage of the scene under observation superimposed onto a visible imageof the scene under observation, wherein the combined signal correspondsto the output image displayed by the display device.
 11. The system asclaimed in claim 1, wherein the predetermined wavelength at which theilluminator device radiates photons is based on the predetermined gas tobe detected.
 12. The system as claimed in claim 1, wherein theilluminator device is selected from a group comprising an infraredilluminator, and a laser, wherein the infrared illuminator is in theform of a heated electrical filament arrangement, and wherein the laseris in the form of a quantum cascade laser.
 13. The system as claimed inclaim 1, wherein; the handheld camera housing defines a thermallyinsulated compartment for enclosing the infrared camera arrangement andthe processing arrangement; the system comprises a cooling arrangementto cool components of the system in the housing; and the housingcomprises an eyepiece aligned with the display device so that a user isable to view the display device within the handheld camera housing viathe eyepiece.
 14. The system as claimed in claim 1, wherein the systemcomprises a laser pointer to assist a user to orient the system to thescene under observation.
 15. A method of detecting a predeterminedtarget gas, wherein the method comprises: radiating, by an illuminatordevice, photons at a predetermined wavelength, at or around anabsorption wavelength of the predetermined target gas selected fordetection, towards a scene under observation in a strobed fashion at apredetermined strobing frequency such that photons at the predeterminedwavelength are radiated to the scene under observation, and photons atthe predetermined wavelength are not radiated to the scene underobservation in an alternating fashion according to the predeterminedstrobing frequency; acquiring, by an infrared camera arrangement,infrared images from the scene under observation at a predeterminedframe rate, wherein the predetermined frame rate is associated with thepredetermined strobing frequency such that active infrared images areacquired while photons at the predetermined wavelength are radiated tothe scene under observation, and passive infrared images are acquiredwhile photons at the predetermined wavelength are not radiated to thescene under observation in an alternating fashion at the predeterminedframe rate; storing, by a data storage device of a processorarrangement, at least one prior infrared image acquired from the sceneunder observation during a prior state of the illuminator device,wherein the at least one prior infrared image is either an activeinfrared image or a passive infrared image, comparing, by at least oneprocessor of the processor arrangement, at least one current infraredimage, acquired during a current state of the illuminator device that isdifferent from the prior state, with the stored at least one priorinfrared image, wherein the at least one prior current infrared image iseither a passive infrared image or an active infrared image; generating,by the at least one processor of the processor arrangement, an outputsignal in response to said comparison, wherein the output signal isrepresentative of an amount of illuminator photon flux absorbed by thepredetermined target gas; and displaying, by a display device of theprocessor arrangement, an output image on a display device based atleast on the generated output signal so as to facilitate detection ofthe particular predetermined target gas, wherein the infrared cameraarrangement and the processing arrangement are located in a handheldcamera housing.
 16. The method as claimed in claim 15, wherein thepredetermined frame rate is associated with the predetermined strobingfrequency in that the predetermined frame rate is an even multiple ofthe predetermined strobing frequency, wherein the predetermined framerate is at least four times the predetermined strobing frequency, andwherein the infrared camera arrangement acquires multiple activeinfrared images and multiple passive infrared images in each strobingcycle of the strobing frequency.
 17. The method as claimed in claim 15,wherein the method comprises: acquiring visible light images of thescene under observation; combining the generated output signal with asignal representative of an acquired visible light image to generate acombined signal representative of an image of the scene underobservation superimposed onto a visible image of the scene underobservation; and displaying the combined signal on the display device.18. The method as claimed in any claim 15, wherein the method comprises:collecting photons from the scene under observation with a lens having afield of view; projecting, with the lens, photons collected to adetector; filtering photons projected from the lens with an opticalfilter thereby to allow only projected photons at the predeterminedwavelength to pass through to the detector; generating electricalsignals in response to filtered photons of the predetermined wavelengthbeing received by the detector; and generating an infrared image of thescene under observation based on the electrical signals received fromthe detector, wherein the generated infrared image is the acquiredinfrared image.
 19. The method as claimed in claim 18, wherein themethod comprises cooling the detector to, and maintaining the detectorat, a temperature between a range of approximately 60K and 75K; orwherein the method comprises cooling the optical filter to, andmaintaining the optical filter at, a temperature between a range ofapproximately 85K and 95K.
 20. One or more non-transitorycomputer-readable storage media storing instructions that, when executedby one or more processors, cause: radiating, by an illuminator device,photons at a predetermined wavelength, at or around an absorptionwavelength of a predetermined target gas selected for detection, towardsa scene under observation in a strobed fashion at a predeterminedstrobing frequency such that photons at the predetermined wavelength areradiated to the scene under observation, and photons at thepredetermined wavelength are not radiated to the scene under observationin an alternating fashion according to the predetermined strobingfrequency; acquiring, by an infrared camera arrangement, infrared imagesfrom the scene under observation at a predetermined frame rate, whereinthe predetermined frame rate is associated with the predeterminedstrobing frequency such that active infrared images are acquired whilephotons at the predetermined wavelength are radiated to the scene underobservation, and passive infrared images are acquired while photons atthe predetermined wavelength are not radiated to the scene underobservation in an alternating fashion at the predetermined frame rate;storing, by a data storage device of a processor arrangement, at leastone prior infrared image acquired from the scene under observationduring a prior state of the illuminator device, wherein the at least oneprior infrared image is either an active infrared image or a passiveinfrared image, comparing, by at least one processor of the processorarrangement, at least one current infrared image, acquired during acurrent state of the illuminator device that is different from the priorstate, with the stored at least one prior infrared image, wherein the atleast one current infrared image is either a passive infrared image oran active infrared image; generating, by the at least one processor ofthe processor arrangement, an output signal in response to saidcomparison, wherein the output signal is representative of an amount ofilluminator photon flux absorbed by the predetermined target gas; anddisplaying, by a display device of the processor arrangement, an outputimage on a display device based at least on the generated output signalso as to facilitate detection of the particular predetermined targetgas, wherein the infrared camera arrangement and the processingarrangement are located in a handheld camera housing.